Section 1- Introduction

The Numerical Electromagnetics Code (NEC-2) is a user-oriented computer code for analysis of the electromagnetic response of antennas and other metal structures. It is built around the numerical solution of integral equations for the currents induced on the structure by sources or incident fields. This approach avoids many of the simplifying assumptions required by other solution methods and provides a highly accurate and versatile tool for electromagnetic analysis.

The code combines an integral equation for smooth surfaces with one specialized to wires to provide for convenient and accurate modeling of a wide range of structures. A model may include nonradiating networks and transmission lines connecting parts of the structure, perfect or imperfect conductors, and lumped element loading. A structure may also be modeled over a ground plane that may be either a perfect or imperfect conductor.

The excitation may be either voltage sources on the structure or an incident plane wave of linear or elliptic polarization. The output may include induced currents and charges, near electric or magnetic fields, and radiated fields. Hence, the program is suited to either antenna analysis or scattering and EMP studies.

The integral equation approach is best suited to structures with dimensions up to several wavelengths. Although there is no theoretical size limit, the numerical solution requires a matrix equation of increasing order as the structure size is increased relative to wavelength. Hence, modeling very large structures may require more computer time and file storage than is practical on a particular machine. In such cases standard high-frequency approximations such as geometrical optics, physical optics, or geometrical theory of diffraction may be more suitable than the integral equation approach used in NEC-2.

NEC-2 retains all features of the earlier version NEC-1 except for a restart option. Major additions in NEC-2 are the Numerical Green's Function for partitioned-matrix solution and a treatment for lossy grounds that is accurate for antennas very close to the ground surface. NEC-2 also includes an option to compute maximum coupling between antennas and new options for structure input.

This manual contains instructions for use of the NEC-2 code and sample runs to illustrate the output. The sample runs lay also be used as a standard to check the operation of a newly duplicated or modified deck. There are two other manuals for NEC-2: Part I: NEC Program Description - Theory (ref. l); and Part II: NEC Program Description - Code (ref. 2). Part I covers the equations and numerical methods, and Part II is a detailed description of the FORTRAN code.